1. Field of the Invention
The present invention relates to a method for manufacturing a silicon carbide semiconductor device, more particularly, a method for manufacturing a silicon carbide semiconductor device including the step of forming a gate insulating film on a silicon carbide substrate.
2. Description of the Background Art
In recent years, in order to achieve high breakdown voltage, low loss, and the like in a semiconductor device, silicon carbide has begun to be adopted as a material for the semiconductor device. Silicon carbide is a wide band gap semiconductor having a band gap larger than that of silicon, which has been conventionally widely used as a material for semiconductor devices. Hence, by adopting silicon carbide as a material for a semiconductor device, the semiconductor device can have a high breakdown voltage, reduced on-resistance, and the like. Further, the semiconductor device thus adopting silicon carbide as its material has characteristics less deteriorated even under a high temperature environment than those of a semiconductor device adopting silicon as its material, advantageously.
An exemplary semiconductor device employing silicon carbide as its material is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). In the MOSFET, a gate insulating film made of silicon dioxide is formed on a silicon carbide substrate. Interface states are formed between the silicon carbide substrate and the gate insulating film made of silicon dioxide. The interface states result in decrease of mobility. For example, WO 2010/103820 describes that in order to inactivate interface states, heating treatment is performed in nitrogen monoxide gas or dinitrogen monoxide gas. According to the method described in WO 2010/103820, the heating treatment is performed under conditions that nitrogen and nitrogen monoxide are mixed at a ratio of 1:1 to 1:9.
However, a MOSFET manufactured using this method does not have sufficiently high mobility.